Synthesis of proposed new compounds will be completed and these and others recently prepared will be evaluated as aromatase (estrogen synthetase) inhibitors in vitro. We will also complete antiovulatory testing in the rat and determine hormonal activity of active compounds and whether they inhibit ovarian estrogen secretion. Studies on poscoital effects with our best inhibitors will be finished. We will determine whether inhibiting ovulation with aromatase inhibitors affects subsequent cycles, fertility and development of progeny in the rat. As estrogen is believed to be required for the maintenance of the corpus luteum in the rabbit, we will carry out studies to determine if aromatase inhibitors will cause regression of the corpus luteum in this species. Using tritium labeled aromatase inhibitors, we will complete studies to determine the metabolic fate of these compounds in the rat.